1. Field of the Invention
The invention relates to a device for receiving formwork elements for the manufacture of concrete structural parts.
In the production of precast concrete parts, the formwork elements in the concrete works are normally arranged on vibrating tables which serve for compacting the concrete cast for forming purposes, using the formwork elements. Such a vibrating table usually consists of a carrying structure comprising steel bearers and of a steel plate forming the table plate. To make it simpler to remove the formwork and to lift off the fully hardened concrete parts, vibrating tables are often designed with a tiltable table plate. The vibrating tables are usually equipped with an exciter in the form of external vibrators which are arranged so as to be distributed over the table plate and which can set the carrying structure composed of the steel bearers and of the table plate in vibration. The external vibrators have electromotively, pneumatically or hydraulically driven flyweights and are mounted in a suitable way in the carrying structure of the vibrating table. After the forming formwork elements have been built up on the vibrating table plate and the fresh concrete has been cast into the formwork elements and into the reinforcements often inserted into these, the external vibrators are set in motion, thus giving rise to complex forms of vibration in the carrying structure and, in particular, in the vibrating table plate which result in the concrete being compacted. In the known vibrating tables, the vibratory energy introduced into the concrete is distributed more or less unequally. The carrying structure supporting the vibrating table plate is excited by the external vibrators mounted there, just as is the table plate, thus resulting in jarring knocks between parts of the carrying structure and in complex transmission and propagation of sound into the air which has a considerable adverse effect on the working conditions of the labor force and may pollute the environment in a way detrimental to health. Sound pressure values of more than 100 dba are often reached.
In order to reduce the very annoying high sound level in precast concrete works when vibrating tables operated by means of external vibrators are used, the following measures have already been put into practice:
a) Optimization of the position and frequency of the external vibrators, the aim also being, in particular, to avoid resonant frequencies, PA0 b) Stiffening of the carrying structure of the vibrating tables and improvement in the connections between carrying elements in order to avoid jarring knocks, PA0 c) Use of insulating material in order to have a positive influence on the sound transition, PA0 d) Use of vibration-absorbing materials between the elements of the carrying structure in order to avoid solidborn sound transmissions, and PA0 e) Vibrational uncoupling of the carrying structure from the ground and force or displacement excitation in a horizontal plane at low frequencies, in order to avoid generating high frequencies which are particularly annoying.
The above mentioned measures are effective, individually or in a suitable combination, for reducing the generation of noise in the vicinity of the vibrating tables. Their subsequent use on existing vibrating tables, not equipped or only inadequately equipped with measures for sound reduction, necessitates complicated additional work and requires complicated changes to the system. Moreover, the improvements capable of being achieved thereby are very limited, apart from the use of the horizontal vibrating or gyro technique which, again, presents problems in achieving a sufficient compacting performance and is therefore not acknowledged.
2. Description of the Related Art
EP-A-0,251,150 shows a device for receiving formwork elements for the manufacture of concrete structural parts, with a static carrying structure and with a sheetlike formwork shell connected to the latter and capable of being set in vibration by a vibrator in order to compact the still plastic concrete. Damping spacer elements are inserted between the formwork shell and the static structure. The vibrator engages the formwork shell, bypassing the spacer elements.